Porcelain Fragile

[AttnAttack]

Once upon a time there was a doll,   // Classic, fairy tale beginning, but its also very overplayed.  Keep that in mind.
with cracked porcelain skin, sharp and fragile.  //as other commentator put, theres a lot of heft to this line.  Lot of emphasis on "broken" imagery and words.
Broken, the doll lived day to day just trying not to fall apart,    //I like the metering here.  Sounds nice, but almost prose-like rather than poetic
but the pieces were sharp, and they hurt        //could be phrased better than "they hurt".  The simplicity of "they hurt" makes me believe the speaker is a child
Day by day she glued herself back together. Cracked but whole.

But The world was cruel, and it found her broken once more.   // Good use of white space

Day by day she glued herself together again. Stronger than before.  // Remove the word "again".  its unnecessary and screws up the metering.
Days turned to years, her fragile skin of porcelain  // this enjambment doesn't flow well into the next line.  Consider a em-dash or a semi-colon. 
a carefully crafted shell of glue and broken shards   // try changing carefully to careful to fix the metering here.
She used it like armor, for her skin was porcelain fragile.  // not sure this makes sense.  She glued her skin back together to wear as armor over her skin?  

One day the cruel world she knew changed.  // remove the word cruel.  its unnecessary.  We already know the world was cruel to her.  add "had" between knew and changed.  this will fix the metering issues.
The need for glue and armor was gone  // remove the word "was"
Safe from fears of broken pieces,  // ok
others called for her to shed her armor  // ok

but she found it was deeper than her skin.  // could be a bit more sophisticated.  think on this line
It crept into her cracks and glued her broken bits.  // good

Broken and lost porcelain never found again,  // metering
Replaced with shards of hate and anger,  //  use more sophisticated words here to signify a change in environment; eg loss of innocence and growth into something fierce and incontemptible.
cemented with glue in the fragile porcelain.  //   ending falls flat.  this is the last line.  if this was the only line you wrote, would you be happy with it?

I already edited it a bit... lol

I enjoyed the childlike nature of the speaker, and the theme of lost innocence.  However, I felt like this could have had more elements added to it, especially near the end, that would spruce it up and make it a stronger poem.  Also, pay attention to how many times you use each word; day appears 8 times, broken appears 6, and porcelain 5. You can (and must) accept diversity in your word choice. Welcome to the site!  I hope this helps.